1. Field of the Invention
The present invention relates to a working machine provided with a diesel engine, a variable displacement hydraulic pump, and exhaust gas treatment equipment.
2. Description of the Related Art
Some exhaust gas treatment equipment removes particulate matter (hereinafter, referred to as PM) from exhaust gas of a diesel engine. Such exhaust gas treatment equipment includes a diesel particulate filter or DPF (hereinafter, abbreviated as “the filter” in some cases). Since this type of exhaust gas treatment equipment has a problem with an increase in discharge pressure, which may occur when PM continuously is accumulated on the filter, it is necessary to remove the PM accumulated on the filter for regeneration of the filter.
The filter is regenerated mainly through self-regeneration or compulsory regeneration. The self-regeneration spontaneously occurs when exhaust temperature reaches a temperature at which PM burns (hereinafter, sometimes called “the regenerative temperature”). The compulsory regeneration is performed by burning unburned fuel contained in exhaust gas to compulsorily increase the exhaust temperature to a regenerative temperature. In addition, the compulsory regeneration includes a method (automatic regeneration) for automatically carrying out regeneration when a certain condition is met (e.g. when an estimated accumulated amount of PM exceeds a predetermined threshold level) and a method (manual regeneration) for carrying out regeneration at arbitrary timing based on operator's operation.
Incidentally, the compulsory regeneration includes a method for allowing exhaust gas to contain unburned fuel by use of multi-injection or post-injection in which fuel injection timing is more retarded than usual. For use of this method, however, if engine cooling-water temperature is low and so temperature in an engine cylinder is low, flame-out will occur, which may lead to a problem of deteriorating drivability or causing white smoke (hereinafter, sometimes abbreviated as “flame-out or the like”).
To prevent the occurrence of flame-out or the like as mentioned above, JP-2005-282478-A describes that if cooling water temperature is lower than a temperature Tw0, which is set lest that the flame-out or the like occurs, then warm-up operation of the engine is continuously performed until the cooling-water temperature reaches the preset temperature Tw0, and compulsory regeneration is then started.